Horizontal curve sawing apparatus

ABSTRACT

A saw for cutting a cant by sensing the curvature of the cant and raising or lowering the saw blade in order to follow the curvature when cutting the cant.

This application is a continuation-in-part of U.S. Utility applicationSer. No. 10/317,896, filed Dec. 12, 2002 now abandoned, which claimspriority from U.S. Provisional Application Ser. No. 60/360,591, filedFeb. 28, 2002, both of which are hereby incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to a sawing apparatus for cutting a cantalong a curve. More particularly, it relates to a sawing apparatus whichsenses the curvature of a cant along a smooth (or sawn) side of the cantand adjusts the saw head by raising or lowering the saw head so as tocut a board of a preset thickness, following the curvature of the cant.

In prior art cant cutting saws, such as that described in Kenyon (U.S.Pat. No. 4,127,044), the vertically oriented saw head remains stationary(is not moved up or down or sideways) while the cant is displacedhorizontally so that the cant may be cut following the curvature of thecant. A sensing roller 25 (also referred to as a surface locator) sensesthe curvature on the wany side of the cant (not the smooth, sawn side),and an orienting pressure roller 6 pushes on the cant based on thefeedback from the sensing roller 25, thus guiding the cant through thesaw head so as to cut the cant while following its curvature. A controlpressure roller 13 offers a degree of resistance to the force exerted onthe cant by the orienting pressure roller 6.

In Kenyon, the cant is oriented with its curvature on the side insteadof on the bottom. However, the smooth (sawn) sides of the cant are ontop and on the bottom of the cant. Therefore, the sensing of thecurvature is done on the wany side of the cant, which is rough, havingbumps and other irregularities that are not present on a smooth, sawnsurface. The resulting cut, which follows that rough surface, will alsobe rough, attempting to conform the cut to all those irregularities inthe surface.

Kenyon requires applying a lateral orienting pressure on the work piece.Kenyon moves the cant to orient it so that the fixed position saw bladescut along the curvature. In Kenyon, once the trailing edge of the canthas gone past the cant orientation means (the orienting pressure roller6), the cant can no longer be shifted laterally to line up the sawblades with the curvature of the cant, so control is lost toward the endof the cut. This means that the end portion of the cut board frequentlywill not have the correct thickness and will have to be scrapped.Furthermore, the cant is moved laterally by the orienting pressureroller 6 which is also acting against the wany side of the cant, whichresults in a less accurate alignment of the cant relative to the sawblades and the relative to the curvature of the cant. Kenyon attempts tominimize this adverse effect (refer to FIG. 3) by having the point ofcontact of the orienting pressure roller 6 a with the cant as close aspossible to the edge(s) closest to the smooth (sawn) surface, and (referto FIG. 5) by using more than one orienting pressure roller 6 a, 6 b andaveraging the input from these multiple rollers.

In Kenyon, the sensor must be facing the concave side of the cant. Thedesign will not work if the sensor 25 is facing the convex side of thecant, because the orienting pressure roller 6 can only push the cantaway from the sensor 25; it cannot pull the board toward the sensor, aswould be required to maintain a constant thickness if the sensor were onthe convex side of the cant. Therefore, the cant must be properlyoriented relative to the sensor 25 before the cant is fed to this priorart saw. This also means that a cant with a compound curvature (onewhich is concave in a portion of its length and convex in anotherportion of its length) cannot be adequately handled by the saw taught inKenyon.

SUMMARY

In one embodiment of the present invention, shown and described below,the saw head moves to follow the curvature of the cant rather thanmoving the cant relative to a fixed position saw head.

In that embodiment, a cant is placed on the conveyor feed belt of thesaw with the either the concave side or the convex side down. A holddown and feeder assembly assists in feeding the cant through the saw. Asensing means (in this example a shoe) senses the position of the bottomsurface of the cant directly underneath the saw head, so as to sense thevertical displacement of the cant relative to the feed belt due to thebowing or curvature of the cant at the saw head. The sensing meanstransmits this information, via a linkage mechanism, to a slidingmagnetic pick-up device. This device is mounted along a probe which isattached to the saw head and which senses the position of the magneticdevice relative to a target position and sends a signal to aprogrammable logic controller which, in turn, causes the saw head tomove up and down to follow the curvature of the cant.

Therefore, as the cant is fed through the saw, if the bottom surface ofthe cant has a concave bow, for instance, the shoe (which is biasedupwardly toward the bottom of the cant) moves up. The programmable logiccontroller will then cause the saw head to move up an equal distance,maintaining the thickness of the board that is being cut.

Other displacement sensing devices, such as electrical, optical, orlaser scanners, for instance, may be used to sense the curvature of thecant, and this curvature may be measured at either the bottom surface ofthe cant, which lies on the conveyor, or at the opposite, top surface ofthe cant. In either case, the saw head would be moved up and down tofollow the curvature of the surface being sensed, in order to maintainthe thickness of the cut board. Both the top and bottom surfaces of thecant are smooth, sawn surfaces.

It should be noted that the displacement sensor (i.e. the shoe) islocated directly below (or above) the saw blade for greatest accuracy.For a mechanical sensor, such as a shoe, it may be easier to track thedisplacement of the cant on the bottom surface, because there is nointerference from the saw. However, if the sensor does not have tophysically touch the cant, such as when the sensor is an optical orlaser scanner, this measurement may just as readily be taken at the topsurface of the cant, directly above the saw blade.

In the embodiment shown and described below, the sensor (the shoe) has abiasing mechanism to keep the shoe against the bottom surface of thecant. In this same embodiment, this biasing mechanism is an aircylinder. However, the biasing mechanism could be a simple spring orother biasing means. When the air cylinder is not actuated, the shoelies flush with the top of the conveyor feed belt. Any target positionset at this time simply defines the thickness of the cut relative to thefeed conveyor, and this dimension remains fixed (the saw head will notbe raised or lowered during the cut). However, if the air cylinder isactuated, the shoe will follow the bottom contour of the cant, meaningthat the saw head will also follow this same contour at the targetthickness (or target position) and the saw will cut a constant thicknessboard off of the cant, following the curvature of the cant.

As soon as the cant reaches the saw blade, the sensor can immediatelybegin sensing the position of the bottom surface of the cant, and theprogrammable logic controller can begin making corresponding correctionsto the position of the saw head in order to follow the contour of thecant from the first end to the last end. There is no loss of control atany point throughout the entire length of the cut.

The smooth (sawn) side of the cant is placed on the conveyor, but thisside can be either convex or concave, or it can, in fact, have acompound curvature, including both concave and convex portions atdifferent points along its length. The saw can accommodate any of theseconditions without requiring any further alignment of the cant relativeto the displacement sensor. The sensing by the displacement sensor isdone on the smooth side of the cant, not on the wany side, resulting ina smooth, accurate cut.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a cant saw made in accordance with the presentinvention;

FIG. 2 is the same view as FIG. 1 but with a cover on the saw frameremoved for clarity in order to show the double knuckle mechanism usedto raise and lower the saw head;

FIG. 3 is a partially exploded, perspective view of the cant saw of FIG.1, detailing the cant hold down mechanism;

FIG. 4 is a partially exploded, perspective view of the cant saw of FIG.1, detailing the parts of the conveyor mechanism;

FIG. 5 is a partially exploded, broken away, perspective view of thecant saw of FIG. 1, detailing the cantilevered mechanism with fulcrumand double knuckle arrangement to raise or lower the saw head;

FIG. 6 is a partially exploded, perspective view of the cant saw of FIG.1, detailing the saw head;

FIG. 7 is a partially exploded, broken away, perspective view of thecant saw of FIG. 1, detailing the sensing shoe and magnetic pick-upsensor mechanism;

FIG. 8 is a side view, similar to FIG. 1, but showing a cant as it isfed and cut, and with some of the covers removed for clarity, in orderto show the sensing shoe mechanism as well as the mechanism to raise andlower the saw head;

FIG. 9 is a schematic showing the relationship between the magneticpick-up device, the probe (which is mounted to the saw head), theprogrammable logic controller, a switch, and the piston actuator;

FIG. 10 is a side view, similar to that of FIG. 8, but for a secondembodiment of a cant saw made in accordance with the present invention;and

FIG. 11 is a side view, similar to that of FIG. 8, but for a thirdembodiment of a cant saw made in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 through 8 show a cant saw 10 made in accordance with the presentinvention. Referring briefly to FIG. 8, the cant saw 10 includes aconveyor table 12 with a frame including legs 14, a hold down and feederassembly 16, a horizontally cutting saw head 18, and a cant curvaturesensing shoe 20. A linkage mechanism 22 connects the sensing shoe 20 toa sliding magnetic pick-up mechanism 24, which slides inside a probe 26that is fixed relative to the saw head 18. A programmable logiccontroller 24 (shown in FIG. 9) receives a signal from the probe 26 and,in turn, sends a signal to a piston actuator 28 to extend or retract inorder to raise or lower the saw head 18 via an actuator arm 30 whichpivots about a fulcrum 32. The actuator arm 30 is connected at one end30A to the piston actuator 28, and it is connected at the other end 30Bto a first pivot shaft 84, which is connected to a saw head lift shaft90 through a double knuckle arrangement 36. The saw head lift shaft 90is fixed to a connecting rod 34 (see FIG. 6), which is fixed to the sawhead 18, as described in more detail below.

Referring to FIG. 8, the cant 38 is fed into the saw 10 traveling fromleft to right, as shown by the arrow 39. The hold down assembly 16(shown in detail in FIG. 3) pushes down against the top surface of thecant 38 as the cant is fed into the saw blade 40, ensuring that the cantis always pressed downwardly against the top surface of the conveyor 12.(Of course, the weight of the cant 38 also helps hold the cant 38 downagainst the top surface of the conveyor 12.)

Referring to FIG. 3, the hold down assembly 16 includes a mounting frame42 defining pivot supports 44 for mounting the bearings 50 for the stubaxles 46 of the substantially “L” shaped hold down bracket 48. Thisallows the free end 48A of the hold down bracket 48 to pivot up and downrelative to the stub axles 46. A pneumatic cylinder 52 has its first endsecured to the hold down bracket 48 via a first shaft 54 secured to thebracket 48. The second end of the cylinder 52 is secured to the conveyortable 12 via a second shaft 56, secured to the conveyor table 12. Theair pressure in the cylinder 52 may be controlled to adjust the pressurebiasing the free end 48A of the bracket 48 downwardly, toward theconveyor table 12. This, in turn, controls the force with which the holddown assembly 16 pushes the cant 38 against the conveyor table 12.Toothed rollers 58 (shown also in FIGS. 1, 2, and 8) contact the sawntop surface of the cant 38 to provide a smooth but positive rollingcontact between the hold down assembly 16 and the cant 38. Of course,other biasing means, such as a spring, or hydraulically or electricallyactuated pistons, could be used in place of the pneumatic cylinder 52.

Referring to FIG. 4, the conveyor table 12 includes geared sprockets 62which engage a plurality of conveyor belts 64 at one end of the conveyorbelts 64. The sprockets 62 rotate with a shaft 66 rotatably supported bybearings 68 mounted on the conveyor table 12. A drive motor 60 at theother end of the table 12 drives a similar set of sprockets (not shown)to drive the conveyor belts or chains 64, causing them to travel alongtracks 70. As will be explained in more detail later, the sensing shoe20 projects upwardly through a gap between two adjacent conveyor belts64 in order to contact the horizontal sawn bottom surface of the cant 38and track the vertical displacement of that horizontal surface of thecant relative to the top surface of the conveyor.

Referring to FIG. 5, a saw head lifting mechanism 72 is used to raiseand lower the saw head 18 to ensure that the saw blade 40 follows thedisplacement of the cant 38 in order to maintain a set thickness of theboard that is being cut. A pneumatically actuated cylinder 28 isconnected at its first end 28A to the conveyor table 12 and at itssecond end 28B to the first end 30A of the lever arm 30. The lever arm30 is part of a pivotable framework 74. This framework 74 includes amain pivot shaft 76, which is rotatably supported by bearings 78 mountedon the inside of panels 80 which are, in turn, secured to the frame ofthe conveyor table 12 as shown in FIGS. 1 and 2. Two parallel side arms82 link the main pivot shaft 76 to a lower knuckle pivot shaft 84, whichis supported at its ends for rotation by two lower knuckle bearings 86.The saw head lift shaft 90 is supported for rotation at its ends by twoupper knuckle bearings 88, which are secured, as by bolts (not shown),to the lower knuckle bearings 86.

This double knuckle mounting arrangement allows for misalignment betweenthe lower knuckle pivot shaft 84 and the saw head lift shaft 90 as thesaw head 18 is raised and lowered. Since the axial position of the mainshaft 76 is fixed relative to the panels 80 and the saw frame 14, andsince the arm 30 pivots with the main shaft 76, the lower pivot shaft 84defines a slight arc as the lever arm 30 pivots. At the same time, thesaw head lift shaft 90 is restricted to travel along a straight verticalline, since, as shown in FIG. 6, the saw head lift shaft 90 is fixed tothe connecting rods 34, which slide vertically within a fixed frame 34A,shown in FIGS. 1, 2, and 8. As the connecting rods 34 move up and down,they raise and lower the saw head.

The double knuckle mounting arrangement, with the two sets of bearings86, 88 fixed together, permits the lower pivot shaft 84 to lie directlybelow the saw head lift shaft 90 at one point along its travel, as shownin FIG. 5, and it allows the lower pivot shaft 84 to be displaced in ahorizontal direction relative to the saw head lift shaft 90, as shown inFIG. 2, so that the lower pivot shaft 84 can follow an arcuate pathwhile the saw head lift shaft 90 follows a vertical path.

Referring to FIG. 6, the saw head 18 includes a motor 92 driving a drivewheel 94 via a drive belt 96 and pulley 98. The saw blade 40 is aflexible blade that extends around the drive wheel 94 and around anidler wheel 100. The motor 92 mounts to a motor mount 102, which alsoincludes two spindles 104 which support the drive and idler wheels 94,100 for rotation. A stationary safety cover 106 is also mounted on thespindles 104. As discussed above, the saw head 18 is fixed, via theconnecting rods 34, to the saw head lift shaft 90.

The connecting rods 34 are guided and constrained to vertical travel bythe tracks 34A, best seen in FIG. 7. The tracks 34A are mounted onhorizontal cross members 108 of the conveyor table 12. The connectingrods 34 raise and lower the saw head 18 as they travel up and down inthe tracks 34A, driven by the piston actuator 28, as will be discussedin more detail later.

FIG. 7 also shows the linkage mechanism 22, which includes a sensingshoe 20 that senses the vertical displacement of the bottom surface ofthe cant relative to the top surface of the conveyor table 12. Thesensing shoe 20 is fixed to an “L” shaped linkage 112. A pivot shaft 110extends through a first end of the shoe 20 and through a first end 112Aof the linkage 112 and is supported at its ends for rotation by bearings114, which are mounted to the conveyor table 12. The shoe 20, linkage112, and pivot shaft 110 pivot together relative to the conveyor table12. The elbow 112C of the L-shaped linkage 112 extends through a sideopening 116 in side wall of the conveyor table 12, so the first end 112Aof the linkage 112 is inside the side wall and the second end 112B ofthe L-shaped linkage 112 is outside the side wall. A pneumatic cylinder118 is secured to the second end 112B of the L-shaped linkage 112. Thepneumatic cylinder 118 pulls down on the second end 112B of the linkage112, which in turn, biases the shoe 20 to a raised position, where itprojects upwardly through a gap between the conveyor belts 64, so as tocontact the sawn bottom surface 38B of the cant 38 and detect itscurvature (See FIG. 8). Of course, other biasing means, such as aspring, or hydraulically or electrically actuated pistons, could be usedin place of the pneumatic cylinder 118.

A slender rod 120 extends vertically, with its first end 120A connectedto the second end 112B of the L-shaped linkage 112, and its second endattached to a sliding magnetic pick-up 24, which is slidably housed in aprobe 26 (See FIG. 8) that is fixed to the saw head 18. The magneticpick-up 24 is able to slide up and down inside the probe 26 such thatthe position of the magnetic pick-up 24 relative to the probe 26 changesdepending on the following conditions:

First, as the shoe 20 rotates about the pivot shaft 110, the linkage 112rotates with the shoe 20, causing the second end 112B of the L-shapedlinkage 112 to move up and down, thereby raising and lowering themagnetic pick-up 24 within the probe 26.

Second, as the piston actuator 28 extends and retracts, the lever arm 30and its side arms 82 move accordingly, raising and lowering the doubleknuckle arrangement 36 which, in turn, raises and lowers the saw head 18(via the connecting rods 34). Since the probe 26 is secured to the sawhead 18, the probe 26 also moves up and down with the saw head 18,changing the position of the magnetic pick-up 24 relative to the probe26.

The shoe 20 defines a convex cant-contact-surface 20A to help it slidesmoothly along the bottom surface 38B of the cant 38. The convex shapealso increases the probability that only one point of the surface 20Awill be in contact with the bottom surface 38B of the cant 38 at anygiven time, and this one point is preferably located directly below theblade 40 (or very close thereto) in order to enhance the accuracy of themeasurement of the curvature of the cant at the leading edge of the cutof the blade 40. Of course, other shapes of sensing shoes, such asrollers, for instance, may be used instead of the convex surface 20A.

Operation of the Cant Saw

referring to FIG. 8, the saw head 18 of the cant saw 10 is firstadjusted so that the saw blade 40 is raised to a preset, desired boardthickness above the top surface of the conveyor belts 64. This presetdistance is the target position for the saw head 18. This presetthickness also is programmed into the programmable logic controller.

A cant 38 is placed on the conveyor table 12 with one of its smooth (orsawn) surfaces 38A facing up and the other smooth surface 38B facingdown, and the cant is fed through the saw blade 40 in the direction ofthe arrow 39 by means of the conveyor belts on the conveyor table 12.The cant may be placed on the conveyor table 12 with either a convex ora concave side on the bottom surface 38B, and in fact the bottom surface38B may even be both convex and concave; that is, it may be convex for aportion of the cant 38 length and concave for another portion of itslength.

The leading edge 122 of the cant 38 first contacts the rollers 58 of thehold down assembly 16, which is preloaded by the pneumatic cylinder 52(See FIG. 3) to securely press the cant 38 against the conveyor belts 64(See FIG. 4). If the air cylinder 118 is turned on, in order to bias theshoe 70 upwardly against the bottom surface 38B of the cant 38, then asthe cant 38 progresses toward the saw blade 40, the convex surface 20Aof the sensing shoe 20 contacts the bottom surface 38B of the cant 38.Note that if the air cylinder 118 is not turned on, the convex surface20A of the shoe 20 remains flush with the top of the conveyor belts 64and, as explained in more detail below, the saw head 18 will not beraised or lowered as the cant 38 is fed through the cant saw 10. Theresult is a straight cut which is parallel to the flat surface of theconveyor belts 64 on the conveyor table 12, instead of a cut whichfollows the curvature of the cant 38. However, if the air cylinder 118is turned on, the shoe 20 follows the contour of the bottom surface 38Bof the cant 38 and, as explained below, the saw head 18 also followsthis same contour but at the aforementioned target position, maintaininga fixed board thickness and resulting in a cut 128 which follows thecurvature of the cant 38.

Assuming, for instance, that the bottom surface 38B of the cant 38 isconcave (bowed upwardly in the middle), then, as the cant 38 progressesin the direction of the arrow 39 in FIG. 8, this bottom surface 38B willbe spaced above the top surface of the conveyor belts 64 (the cant 38will be supported by the ends of the cant 38 which are still in contactwith the conveyor belts 64). The shoe 20, which is biased upwardly bythe air cylinder 118, also moves up through a longitudinal gap betweenthe belts 64 (See FIG. 7), such that the convex surface 20A of the shoe20 remains in contact with the bottom surface 38B of the cant 38, anddoes so at a point directly below the blade 40. (The statement “directlybelow the blade” is intended to include anything that is substantiallydirectly below the blade, so that the sensor will be causing thecontroller to move the cutting head to the correct position to maintainthe thickness of the cut board.)

The upward movement of the shoe 20 results in a corresponding downwardmovement of the end 112B of the “L” shaped linkage 112, as well as acorresponding downward movement of the magnetic pick-up sensor 24 insidethe probe 26. The programmable logic controller 124, shown schematicallyin FIG. 9, senses the change in position (both magnitude and direction)of the magnetic pick-up sensor 24, and it sends a signal, via the switch126, to the piston actuator 28 to extend, pushing downwardly on the end30A of the arm 30, causing upward movement of the double knucklearrangement 36, and raising the saw head 18. The probe 26 is attached tothe saw head 18, and thus it also moves upwardly.

The programmable logic controller 124 continues to send a signal for thepiston actuator 28 to extend until the probe 26 has moved upwardly anamount equal to the magnitude of the downward movement of the magneticpick-up 24, such that the algebraic sum of the distances moved by themagnetic pick-up 24 and by the probe 26 is equal to zero.

Of course, as the magnitude of the separation between the top surface ofthe conveyor belts 64 and the bottom surface 38B of the cant 38approaches zero (as when the trailing edge of the cant 38 is approachedin the above example of a concave bottom surface 38B), the shoe 20 ispushed downwardly against the biasing action of the pneumatic cylinder118. This results in an upward movement of the end 112B of the linkage112 and a corresponding upward movement of the magnetic pick-up 24. Theprobe 26 sends a signal to the programmable logic controller 124, whichthen sends a signal to the piston actuator 28 to retract so as to lowerthe saw head 18. In this manner, the saw blade 40 makes a cut 128 whichfollows the curvature of the bottom surface 38B of the cant 38.

Other Embodiments

FIG. 10 shows a cant saw 10′ made in accordance with the presentinvention. This cant saw 10′ is very similar to the cant saw 10described above, except that the linkage mechanism 22′ is different andresults in a movement of the magnetic pick-up device 24 which is equalto the movement of the sensing shoe 20, instead of the inverselyproportional relationship of the linkage mechanism 22 of the first cantsaw 10.

In this linkage mechanism 22′, the shoe 20 and its corresponding shoetiming gear 130 pivot about a shoe pivot shaft 132. The “L” shapedlinkage 112′ and its corresponding linkage timing gear 134 pivot about alinkage pivot shaft 136. A timing chain 138 meshes with both the shoetiming gear 132 and the linkage timing gear 134 such that rotation ofeither one of the timing gears 130, 134 results in an identical rotationof the other of the timing gears 130, 134. In this arrangement, thelinkage arm 112′ and the magnetic pick-up 24 are connected via the rod120 and faithfully track the up and down movement of the sensing shoe20. The cylinder 118 is mounted to the L-shaped linkage 112′ and,through the timing chain 138, biases the shoe 20 upwardly. The movementof the magnetic pick-up 24 is equal in direction and distance to themovement of the sensing shoe 20.

In this instance, the programmable logic controller 124 need only signalthe piston actuator 28 to extend or retract until the position of themagnetic pick-up 24 relative to the probe 26 is once again at the targetposition. For instance, should the shoe 20, and therefore the magneticpick-up 24, move up ½ inch, the programmable logic controller instructsthe piston actuator 28 to extend until the saw head 18 (and thus alsothe probe 26 which is attached to the saw head 18) moves up ½ inch, suchthat the position of the magnetic pick-up 24 relative to the probe 26returns to its starting position. Thus, in this instance, the algebraicdifference of the distances moved by the magnetic pick-up 24 and by theprobe 26 is equal to zero.

FIG. 11 shows another embodiment of a cant saw 10* made in accordancewith the present invention. This cant saw 10* is very similar to thecant saw 10′ described above, except that the linkage mechanism 22* usesa linear bearing 140 to provide equal movement of the sensing shoe 20,the linkage arm 112*, and the magnetic pick-up device 24. As in the caseof the cant saw 10′, the movement of the magnetic pick-up 24 is in thesame direction as the movement of the sensing shoe 20. Therefore, theoperation of the programmable logic controller 124 and of the rest ofthe saw head height adjustment mechanism for this cant saw 10* is thesame as that of the cant saw 10′.

While the embodiments described above show several means for sensing thecurvature of a cant and for adjusting the height of the saw blade inorder for the cut to follow this curvature, various other sensing andadjusting mechanisms could be used. For instance, as has already beenmentioned, the sensing could be done on the top surface of the cantinstead of on the bottom surface. Also, the curvature could be sensedvia other sensing devices including rollers instead of a shoe, or evenby using “virtual” sensing devices such as lasers or optical orelectronic sensors. Also, the raising and lowering of the saw head couldbe done directly via linear displacement devices monitored by positionswitches in order to obtain the required movement of the saw head asindicated by the sensing device. It will be obvious to those skilled inthe art that modifications may be made to the embodiments describedabove without departing from the scope of the present invention asdefined by the claims.

1. A saw for cutting a cant along a curved surface, comprising: aconveyor frame defining a substantially horizontal conveying surface forsupporting a cant; a saw head mounted for vertical movement relative tosaid conveying surface; a horizontally cutting saw blade mounted on saidsaw head; a curvature sensor for sensing the displacement of ahorizontal surface of the cant above the conveying surface; a controllerin communication with said sensor; and means for moving said saw head upand down in accordance with a signal from the controller to track thedisplacement of the horizontal surface of the cant in order to maintaina set board thickness, said means for moving said saw head up and downincluding a lift lever mounted for pivoting movement relative to saidconveyor frame; and an actuator connected to a first end of said liftlever and in communication with said controller; wherein said lift leverincludes a pivot shaft at a second end of said lift lever, said pivotshaft being supported for rotation by a pair of pivot shaft bearings:wherein said curvature sensor senses the displacement of the cantsurface directly below said saw blade and includes a shoe mounted forpivoting movement relative to said conveyor frame; a magnetic devicewhich moves along with the shoe: a probe which senses the movement ofsaid magnetic device; and a biasing means which urges said shoe upwardlyinto contact with the bottom surface of the cant; and further comprisinga saw head lift shaft extending parallel to said pivot shaft and fixedrelative to said saw head; said saw head lift shaft being supported forrotation by a pair of saw head lift shaft bearings; wherein said pivotshaft bearings are fixed to said saw head lift shaft bearings,respectively, thereby allowing for horizontal displacement between saidpivot shaft and said saw head lift shaft as said lift lever pivotsrelative to said conveyor frame to raise and lower said saw head.